1. Field of the Invention
The present invention relates to an optical information recording medium and an information recording method capable of recording and reproducing information by using a laser light, and a dye compound suitable for the medium and method. The invention particularly relates to a heat-mode type optical information recording medium and an information recording method suitable for recording of information by using a short wavelength laser light at a wavelength of 450 nm or shorter, and a dye compound suitable for the medium and method.
2. Description of the Related Art
Information recording media (optical disk) capable of recording information only for once by a laser light have been known. The optical disks are referred to also as writing once CD (so-called CD-R). A typical structure thereof comprises a transparent disk-like substrate. The structure also comprises a recording layer comprising an organic dye, a light reflection layer comprising a metal such as gold, and a protective layer made of a resin staked in this order on the substrate. Recording of information on a CD-R is conducted by irradiating the CD-R with a near-infrared layer light (usually, a laser light at a wavelength near 780 nm). The irradiated portion of the recording layer absorbs the light and is locally heated to cause physical or chemical changes (for example, pit formation) and changes its optical characteristics, thereby recording information. On the other hand, reading (reproduction) of the information is also conducted by radiating a laser light at the same wavelength with that of the laser light for recording. Information is reproduced by detecting the difference of the reflectivity between a portion in which the optical characteristics of the recording layer are changed (recording portion) and a portion in which the characteristic are not changed (non-recording portion).
Recently, networks such as the Internet and high-definition TVs have been rapidly spreading. Further, broadcasting of HDTV (High Definition Television) will start in the near future. Needs for large capacity recording media for recording image information easily at a reduced cost have been increased more and more. While CD-R and DVD-R, which enable high density recording by using a visible laser light (630 nm to 680 nm) as a recording laser, are predicted to be used as large capacity recording media in some areas, media having larger capacity than those media will be needed in the future. Optical disks have been developed which have a larger recording capacity with higher recording density owing to use of a laser light at a still shorter wavelength than DVD-R. For example, an optical information recording medium has been sold which is referred to as Blue-ray system and which uses a blue laser at 405 nm.
A method of recording information and reproducing information on an optical information recording medium has been disclosed wherein the recording medium has a recording layer containing an organic dye. The method comprises irradiating the medium with a laser light at a wavelength of 530 nm or shorter from the recording layer side to the light reflection layer side. Specifically, an information recording and reproducing method has been proposed which comprises irradiating an optical disk with a laser light of blue color (wavelength: 400 to 430 nm, 488 nm) or blue green color (wavelength: 515 nm), the disk comprising, for example, a porphyrin compound, azo dye, metal azo dye, quinophthalone dye, trimethine cyanine dye, dicyanovinylphenyl skeleton dye, coumarin compound, or naphthalocyanine compound.
The prior art which discloses dyes usable in the blue laser light recording disks includes the following patent documents: JP-A (Japanese Patent Application Laid-open) No. 2001-287460; JP-A No. 2001-287465; JP-A No. 2001-253171; JP-A No. 2001-39034; JP-A No. 2000-318313; JP-A No. 2000-318312; JP-A No. 2000-280621; JP-A No. 2000-280620; JP-A No. 2000-263939; JP-A No. 2000-222772; JP-A No. 2000-222771; JP-A No. 2000-218940; JP-A No. 2000-158818; JP-A No. 2000-149320; JP-A No. 2000-108513; JP-A No. 2000-113504; JP-A No. 2002-301870; JP-A No. 2001-287465; US-A No. 2002/76648A1; and JP-A No. 2003-94828.
However, according to the study made by the present inventors, the recording characteristics of the optical disks are not satisfactory which include known dyes described in the above-listed patent publications. Accordingly, further improvement is necessary particularly in recording sensitivity.